1. Field of the Invention
The present invention relates to a frequency-phase adjusting device and a related method, and more particularly, to a device and method for lowering instantaneous maximum error and for solving vibration problems by adjusting its frequency and phase at the same time.
2. Description of the Prior Art
Using an oscillator to oscillate an initial frequency and then using a phase locked loop (PLL), a voltage-controlled oscillator (VCO), a digital-controlled oscillator (DCO), or an all digital phase locked loop (ADPLL) to control and generate a desired frequency and phase for a system is a familiar technique. Herein the VCO, the DCO, or the ADPLL is used for providing a digital control code or a control voltage to an analog circuit, so as to generate the corresponding frequency and phase.
In a communication system, demands of catching up the remote-end frequency and phase are often encountered. When using a conventional PLL, it is necessary to catch up the remote-end phase first and then catch up the remote-end frequency by jumping phase. However, at that moment of jumping phase, the received echo/near-end crosstalk of the analog-to-digital converter is corresponding to a current phase, but the echo/near-end crosstalk eliminated by the echo/near-end crosstalk canceller is corresponding to a previous phase, therefore, an instantaneous maximum error occurs, which results in a poor system performance. If a conventional VCO, DCO, or ADPLL is adopted, catching up the remote-end frequency first is necessary. Due to the phase error existing between the both ends, it must catch up with the phase of the opposite side by means of tuning up/tuning down its frequency. By the time when the phase of the opposite side is caught up, its frequency becomes not the same as the opposite side at this time. Hence, the action of tuning down/tuning up its frequency is required once more. For this reason, a vibration phenomenon will easily happen in the system, which may cause a system breakdown.